Method and apparatus for objective electrophysiological assessment of visual function

ABSTRACT

For electrophysiological assessment of visual function, a head mounted stereo display (eg virtual reality goggles) for displaying a stimulus is used to generate a retinal or cortical response. In particular, a method for objective electrophysiological assessment of visual function of at least one eye of a subject includes presenting a visual stimulus to at least one eye of the subject, recording at least one of a retinal response and a cortical response generated as a result of the presenting, analyzing said response and, as a result of said analysing, forming a map of the visual function of the at least one eye of the subject. The invention also relates to a system for such electrophysiological assessment.

TECHNICAL FIELD

This invention relates to the electrophysiological assessment of visualfunction using a head mounted stereo display (eg virtual realitygoggles) for displaying a stimulus which is used to generate a retinalor cortical responses. In paiticular, the integrity of the visual fieldcan be assessed objectively by measuring retinal or cortical responsesto a multifocal visual stimulus presented by a head mounted virtualreality display instead of a conventional monitor. This providesadvantages of space, patient acceptance, standardizing distance to thedisplay, and the possibility of monocular or binocular simultaneousrecording. The invention also describes scaling of the multifocal visualevoked potential (VEP) signals according to backgroundelectroencephalogram (BEG) levels, which reduces inter-individualvariability.

BACKGROUND ART

The objective assessment of the visual field using multi-focalstimulation has been reported recently (refs. 1-7). Using differenttypes of multifocal stimulus presentation (Sutter U.S. Pat. No.4,846,567; Malov, International Patent Application No PCT/AU00/01483 andrefs 14-17, the disclose of which are hereby being incorporated byreference), stimulation of a large number of locations of the visualfield can be performed simultaneously. Visually evoked corticalpotentials (VEP) and electroretinograms (ERG) can be recorded from allareas of the field. For the, VEP various electrode placements have beenused. The best representation of the visual field was reported by theinventors with multichannel bipolar recordings (Klistomer and Graham,International Patent Application No, PCT/AU99/00340). Multifocal ERGrecording has been performod with various electrodes (gold toil, DTL,Birian-Allen, gold lens). Good correlation was reported between themultifocal VEP and visual field loss in glaucoma (refs. 2, 5-7), andbetween the multifocal ERG and local retinal disease (ref 8), but nutbetween the multifocal ERG and glaucoma (ref 9, 10).

However, these recordings require a high resolution, large screendisplay (22 inch or larger), and subjects are required to sit close tothe screen. The distance of the subject from the screen changes the areaof field stimulated, and also changes the focal length and the, therequired spectacle correction, so must be closely controlled during therecording. The CRT monitor also produces a large electromagnetic fieldwhich may affect the recordings when the subject is in close proximityto the screen. Recording is limited to one eye at the time, whereas withgoggles it is possible to present a different stimulus to the two eyesat the same time. Therefore the concept of using head mounted displayprovides, a solution to these problems, and saves significantly on spacerequirements. It also allows for portability of the system. Binocularsimultaneous multifocal recording reduces the recording time up to 50%by allowing two eyes to be tested simultaneously using differentstimulus sequences for the two eyes.

A significant problem with multifocal VEP recordings has been the largeinter-individual variability seen among the normal population, whichlimits the sensitivity of applying values from a normal data base whenlooking for small changes early in the disease process. A scalingalgorithm has previously been reported by us (Klistomer & Grahm,International patent application No. PCT/AU99/00340) which helped toreduce this variability. However, the scaling of VEP amplifies accordingto background electroencephalogram levels as described in this patenthas been reported to be a superior technique for reducinginter-individual variability and increasing the sensitivity of the test.

DISCLOSURE OF THE INVENTION

The derivation of a functional map of the human visual field can beachieved from analysis of either multifocal VEP or ERG responses. TheVEP responses tend to reflect losses at all stages of the visualpathway, whereas the ERG responses tend to correlate with local retinaldisease. It has been demonstrated by Malov, International PatentApplication No PCT/AU00/01483 that using a multifocal stimulus driven bya spread spectrum technique, (such that different parts of the visualfield are stimulated by different random sequences), and by usingappropriately placed recording electrodes on the scalp with multiplerecording channels, that accurate maps of visual function can berecorded in the form of multifocal pattern VEPs. Disease states such asglaucoma or optic nerve disorders that cause blind spots in the vision(eg optic neuritis in multiple sclerosis) can the detected and mapped.Both amplitudes and latencies of the signals can be compared to normalreference values or compared between the two eyes of a subject.

We have found that a head mounted stereo display (eg virtual realitygoggles) can be applied to these recording techniques, providingsignificant advantages. It reduces the space required in the laboratoryor test area by removing the need for a large monitor. It makes the testpotentially portable, and it standardises the distance to the displayreducing problems of refraction, variable head position and thus area offield tested. It removes the problem of electromagnetic noise emanatingfrom the screen when the subject sits close to the monitor. A headmounted stereo display has good patient acceptance, and both monocularor binocular recording can be performed.

Simultaneous binocular recording can be achieved with the application ofthe spread spectrum technique (Malov, International Patent ApplicationNo PCT/AU00/01483) and a head mounted stereo display to providedifferent pseudorandom stimulus patterns to the two eyes at the sametime. The stimulus algorithm is divided inito twice the number ofsegments and these can be distributed between the two eyes, stillproviding different stimulus sequences to each part of the field andwith each subsequent run. The cross-correlations can derive VEP resultsfrom each eye independently, with minimal auto-correlation of thesignals within or between eyes. This has the advantage of shortening thetest time significantly. It also standardises conditions of therecording such that the two eyes are recorded under the same conditionsin terms of the subject's visual attention and extraneous noise levels.This aids in the reliability of direct comparisons between eyes of anindividual.

The invention thus, provides a method and apparatus for objectivelyassessing the visual field using virtual reality goggles to present amultifocal stimulus and then recording of either retinal (ERG) orcortical (VIP) responses to that stimulus. It includes simultaneousbinocular recording of the VEP, using different stimuli for the twoeyes. It also includes a new scaling method to reduce inter-subjectvariability in the recorded multifocal VEP amplitudes by scaling The VBPresponse according to overall electroencephalogram activity.

A suitable head mounted stereo display is what is commonly known asvirtual reality goggles. Other head mounted displays which are able topresent a suitable stimulus which can generate a retinal or corticalresponse would also be appropriate.

“Viral reality” is a term applied to the experience of an individualwhen viewing through a head-mounted display an image presentedimmediately before the eyes which has the appearance of being viewed ata distance from the eye. Different images can be presented to the twoeyes to give a three dimensional effect.

It is a purpose of this invention to provide a method and apparatus forrecording of responses from multiple parts of the visual field usingvirtual reality goggles, and thus provide a compact, portable systemthat is acceptable for the patient and clinician, and removes the needfor close monitoring of recording distances from the viewing screen.

According to one aspect of this invention there is provided a method forobjective electrophysiological assessment of visual function of at leastone eye of a patient, which method comprises presenting a visualstimulus to at least one eye of the patient recording at least oneresultant response, selected from the group consisting of a retinalresponse and a cortical response, generated as a result of thepresenting, analysing said response; and as a result of said analysing,forming a map of the visual function of the at least one eye of thepatient.

Usually, the presenting of the visual stimulus is achieved by a headmounted display, in particular a head mounted stereo display such as ahead mounted virtual reality stereo display.

According to another aspect of this invention there is provided a methodfor objective electrophysiological assessment of visual function, whichmethod comprises placing a head-mounted stereo display for presenting astimulus, on the head of a patient, placing electrodes on the scalp orin contact with the eye of said patient, connecting said head-mountedstereo display to a computer which generates an algorithm for drivingsaid stimulus; generating said stimulus; recording the resultant retinalor cortical responses generated as a result of the stimulus; amplifyingand analysing said responses; and as a result of said analysing, forminga map of the visual function.

According to a further aspect of this invention there is provided amethod of identifying alpha-rhythm spikes or electrocardiogram signalsin raw data by application of Fourier spectrum analysis. (It isimportant to identify these spikes prior to scaling since they may alertthe operator to lack of visual attention of the patient.)

According to a still further aspect of this invention there is provideda system for electrophysiological assessment of visual function of atleast one eye of a patient comprising a head-mounted stereo display forpresenting a stimulus to at least one eye of the patient; electrodesplaced on the scalp or in contact with the eye; a computer whichgenerates an algorithm for driving the stimulus; and a means forrecording at least one resultant response, selected from the groupconsisting of a retinal response and a cortical response, generated as aresult of presenting said stimulus; and means for recording theresultant retinal or cortical responses and software for analysing theretinal or cortical response to said stimulus.

According to another aspect of this invention there is provided a methodfor analysing at least one multifocal visual evoked potential recordingfrom any mode of multifocal stimulation comprising scaling output fromcomputer software according to overall spontaneous brain activity levels(ie. electroencephalogram levels) of a subject during the recording inorder to minimise inter-subject variability. The EEG scaling is morereliable if a method for removing high alpha-rhythm signals orelectrocardiogram contamination is employed when calculating thebackground EEG levels. The mode of multifocal stimulation includesconventional CRT or LCD monitors or plasma screens for example.

As mentioned above, the head-mounted stereo display suitable comprisesvirtual reality goggles. The head-mounted stereo display may be used toderive a signal from the cortical visual evoked potentials. It may alsobe used to derive an electroretinogram signal from the eye. This displayshows any type of multifocal stimulation directly to the eye. Thestimulus presented to the eye may be a flash stimulus or a patternstimulus. The stimulus may vary in luminance, colour or stimulusduration to elicit visual responses. The head-mounted stereo displaysuitably uses a liquid crystal display or plasma screen, for example.The stimulus may be presented monocularly or binocularly. The samestimulus may be presented binocularly for simultaneously recording ofsignal from both eyes. Where different stimuli are presented to the twoeyes, they may be simultaneoulsly presented binocularly forsimultaneously recording to signals from the two eyes. For analysis ofmultifocal visual evoked potential recordings, the results a scaledaccording to the overall spontaneous brain activity (i.e.electroencephalogram levels) of the subject during the recording tominimise variability.

The invention utilises multifocal stimulation techniques. Any multifocalstimulator (either existing equipment such as ObjectiVision, VERIS,Reuscan, or future systems) can be used to generate a stimulus which isthen projected into virtual reality goggles using monocular or binoculardisplays. We have established that both the ObjcctiVision and VERISsystems can be used in recording with visual reality goggles. Thestimulus can be diffuse (flash) or structured (pattern) and can vary inintensity, colour, size or temporal characteristics. Appropriateelectrodes placed on the scalp for the VEP, or in the eye for the ERG,allow for recording of the electrophysiological response, which is thenamplified by a conventional amplifier. Cross-correlation techniques (eg,Malov, International Patent Application No PCT/AU00/01483) allow forderivation of the signal from background noise. A topographical map ofthe responses can then be derive corresponding to the field of view ofthe subject. The output can displayed as a printout of results, andcomparisons made with a nominal data base of responses.

To reduce the inter-individual variability of the multifocal VEPrecordings the inventors have applied a scaling factor based onbackground electroencephalogram (EEG) levels. Scaling of the VEPamplitude based on amplitude of spontaneous brain activity eliminatespart of the variability between individuals caused by differences inconductivity of underlying tissues (eg bone, muscle, skin andsubcutaneous fat). This also reduces the differences seen between malesand females, since it is known that women have generally higheramplitude VEP signals when compared to men, presmably due to sexdifferences in tissue thickness and conductivity. Scaling according toEEG signals removes this difference, rendering final signals equivalentbetween the sexes. By reducing the range of variability between subjectsit improves the sensitivity of the test for detecting abnormality.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of embodiments of the present invention will now be describedwith reference to the drawings in which:

FIG. 1 is a schematic representation of the apparatus for VEP recordingincluding virtual reality goggles;

FIG. 2 is a schematic of the apparatus for ERG recording includingvirtual reality goggles;

FIG. 3 is an example of a muiltifocal multichannel VEP recording from anormal subject using conventional screen (FIG. 3A) and goggles (FIG.3B);

FIG. 4A shows the printout from a subjective Humphrey visual field testwith a scotoma demonstrated in the inferior visual field of the righteye of a glaucoma patient;

FIG. 4B shows a multifocal multichannel VEP recording using virtualreality goggles from the same eye as in FIG. 4A;

FIG. 5 shows the correlation between multifocal VEP amplitude andelectrocencephalogram (BEG) levels during recording;

FIG. 6A shows an example of normal Fourier spectrum of EEG used forscaling VEP results;

FIG. 6B shows a trace with strong alpha-rhythm activity around 8 Hzwhich must be removed before scaling (for example by using a polynomialalgorithm); and

FIG. 6C shows rhythmic electrocardiogram spikes which also need to beexcluded.

DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic of the apparatus of VEP recording using virtualreality goggles (1), which present the display to the subject. Thegoggles are connected to a computer (2) with a linked video board thatgenerates the multifocal stimulus. Recording electrodes on the scalp (5)and a ground reference eletrode (shown on tho earlobe), detect the VEPsignal from one or more recording channels (in this case four channelsare shown). The signals are conducted to an amplifier (3), before beingprocessed by software for presentation on the operators display (4).Results can be compared for each eye, or between the two eyes of asubject with respect to normal reference values.

FIG. 2 shows a schematic of the apparatus for multifocal ERG recordingusing virtual reality goggles (1). The set up is the same as in FIG. 1except that the recording electrode is placed in contact with the eye oreyelid. A ground electrode is required (shown on the earlobe). Only onechannel recording is required for the ERG.

FIG. 3 is an example of multifocal multichannel VEP recording from theright and left eye of a normal subject, FIG. 3A shows the responsesachieved using a conventional screen (22 inch Hitachi monitor) topresent the stimulus. A cortically scaled dartboard stimulus wasgenerated with 60 different areas of pattern stimulation using theObjectiVision perimeter. The trace array shown in the figure representsthe responses generated from each part of the visual field tested out to27 degrees of eccenricity temporally and 34 degrees nasally. Forgraphics purposes the central areas are relatively enlarged to show theraw VEP signal within that are. FIG. 3B shows a multifocal multichannelVEP recordings from the some normal subject as in FIG. 3A, recordedusing virtual reality goggles to present the same stimulus instead ofthe conventional monitor. The same ObjectiVision system was used. Theresponses are of similar order of magnitude in the two techniques,although there is source variation in amplitude across the field. Due tothe specifications of the goggles used, the display was limited to 21degrees temporally and 27 degrees nasally.

FIG. 4 provides a comparison between subjective perimetry findings andthe objective VEP assessment of the visual field using virtual realitygoggles. FIG. 4A slows the grayscale and pattern deviation printout froma subjective Humphrey visual field test of the right eye of a glaucomapatient. An inferior arcuate scotoma (blind spot) is shown in the visualfield. FIG. 4B shows the multifocal multichamnel VEP recording from thesame eye as in FIG. 4A, recorded using virtual reality goggles. Analysisof the signals demonstrates loss of VEP responses corresponding to theinferior scotoma in FIG. 4A, with more extensive reductions in thesuperior field than seen on the Humphrey. The amplitude deviation plotshades areas according to probability of abnormality when compared to areference range of normal values extrapolated from the reconventionalscreen ObjectiVision system. This suggests that the technique is capableof detecting visual field loss in glaucoma, just as it is with the useof the conventional large screen. It may also demonstrate moresignificant glaucomatous damage than suspected on conventional Humphreyfield testing. Five glaucoma patients have been tested with the virtualreality goggles and the scotomas were detected in all five cases.

Examination of multifocal VEP data from normal subjects usingconventional CRT monitors demonstrated that the amplitude of themulti-focal VEP is not age-dependant (contrary to most electrophysiologyparameters, eg the pattern ERG). In fact, some elderly people produceVEP responses of higher amplitude. Individual variation in the thicknessof the scalp or subcutaneous tissue may cause inter-individualdifferences in VEP amplitude due to variable impedence of bone and fat.Direct measurement of the thickness or impedance of these tissues is notcurrently practical. However, the impedance will also affect theamplitude of the spontaneous brain activity (EEG) in a similar fashionto the VEP. To confirm this we conducted a study using the ObjectiVisionVEP perimeter of the correspondence between spontaneous EEG amplitude(99% confidence interval) and multifocal VEP amplitude (largestamplitude of a trace). The study included 34 normal subjects. Theresults demonstrated a strong correlation between the EEG amplitude aidVEP (correlation coefficient r=0.81). The scatterplot for thecorrelation is shown in FIG. 5. An alternative method to measurebackground EEG activity is to calculate a Fourier power spectrum of theEEG.

Therefore, if the level of spontaneous EEG activity is calculated duringthe recording. it provides an indirect measure of the overallregistration of brain signals for that individual for the electrodepositions used. Whilst it is recognised that EEG amplitude is determinedby many additional factors other than conductivity, it is proposed thatscaling of an individual's VEP responses according to their EEG levels,relative to normal population EEG values, helps to reduceinter-individual VEP variability.

The EEG amplitude is approximately 1000× the amplitude of the VEP, so itis reasonable to assume that the VEP signals themselves will have littlecontribution to the raw EEG levels. In analysis of multifocal VEPrecordings the EEG raw data is actually examined by cross-correlationtechniques to extract the VEP signals. When recording from anindividual, the overall level of the raw EEG (99% confidence interval)as recorded during each run of the VEP recording, can be used to providean individual's scaling factor. The VEP extracted is then scaled by theEEG scaling factor.

The value of that technique of the invention of VEP scaling wasconfirmed by examining the data from 50 normals. The coefficient ofvariation for all 60 visual field test points had a mean value of 50.1%.When the results were scaled according to background EEG values thecoefficient of variation for all 60 visual field test points wasproduced to 28.2%

By using EEG scaling, the sensitivity of the test was also improved. Ina study of 60 glaucoma cases using the ObjectiVision system formultifocal VEP perimetry, several glaucoma cases were not flagged asabnormal using the unscaled data since the subjects had overall largesignals compared with normal, even though focal relative reductionscould be seen when examining the trace arrays. With the data scaledaccording to EEG levels however, these subjects were identified ashaving localised reductions their VEP amplitudes and the scotomas wereflagged appropriately.

The EEG raw data can contain a large component of alpha rhythm signalsand also spikes of electrocardiogram signals. If these are not excludedfrom the scaling factor applied, then some subjects will have their datainadvenently scaled down lower than is appropriate. This can introducefalse positive results in the VEP. One technique for rectifying thisproblem is to examine the raw signal by Fourier analysis and anyalpha-rhythm spikes and electrocardiogram signals can be identified.These can then be excluded from the spectrum before calculating ascaling coefficient.

Therefore scaling of the VEP amplitude based on amplitude of spontaneousbrain activity eliminates part of the variability between individualscaused by differences in conductivity of tissues. This technique hasapplication in analysing multifocal VEP signals recorded withconventional CRT monitors, plasma screens, LCD screens, or with virtualreality goggles.

INDUSTRIAL APPLICABILITY

The method and system of this invention will find wide use in themedical field, specifically in the field of ophthalmology.

The foregoing describes only some embodiments of the invention andmodifications can be made thereto without departing from the scope ofthe invention.

REFERENCES

-   1. Daseler H A & Sutter E E. Vis Rerearch 1997; 37(6)675-790-   2. Klistomner Al, et al Invest Ophthamol Vis Sci 1998; 39(6):937-950-   3. Kiistomer A J, et al Aust N Z J Ophthalmol 1998;26:91-94.-   4. Graham S L, & Klistomer A. Aust N Z J Ophthalmol 1998;26;71-85-   5. Graham S L, et al Surv Ophthalmol 1999; 43 (Suppll):s199-209-   6. Graham S L & Klistomer A. Curr Opin Ophthalmol 1999;10:140-146.-   7. Graham S L, et al J Glaucoma 2000;9,10-19-   8. Kondo, M, et al Invest Ophthalmol Vis Sci, 1995;36:2146-2150-   9. Vaegan & Buckland L. ANZ J Ophthalmol 1996; 24(2):28-31-   10. Johnson C A, et al J Glaucoma 2000;9(AGS abstract):110-   11. U.S. Pat. No. 4,846,567 (Sutter)-   12. Graham S et al Vol 40 Invest Ophthalmol Vis Sci, 1999, 40(4)    ARVO Abstract #318-   13. U.S. Pat. No. 5,539,482 (James & Maddegs)-   14. Gold IEEE Trans, 1967, V.IT-13 (4)619-621-   15. Sarwata &. Pursley. Proc IEEE, 1980, Vol 68 (5)593-619-   16. Olsen et al IEEE Trans, 1982, V.IT-28(6)858-864-   17. Kanaletdinov B. Problems of Information Transmission, 1988, Vol    23 (2)104-107-   18. Klistomer PCT/AU99/00340

1. A system of simultaneous electrophysiological assessment of visualfunction of two eyes of a head, the head having a scalp, each eye havinga visual field, the system comprising: a device configured tosimultaneously stimulate different portions of the visual field of eacheye with a visual stimulus comprising sequences of different timing orcharacter, wherein the device is configured to binocularly presentdifferent pseudorandom visual stimulus patterns to each of the two eyessimultaneously, each said different pattern for each eye comprisingdifferent stimulus sequences in each said portion of the visual field ofeach eye; electrodes adapted to be placed on the scalp and configured tosimultaneously obtain: overall spontaneous brain activity levelscomprising electroencephalogram levels during said stimulating; andvisual evoked potential (VEP) signals representative of retinalresponses of each of the two eyes to the visual stimulus in each of thestimulated portions of the visual field of each respective eye, whereina signal representative of each of the stimulated portions of the visualfield of each eye are obtained simultaneously; and software forelectrophysiological assessment of the visual function of each of thetwo eyes based on the respective VEP responses of each of the two eyesto the different pseudorandom stimulus visual patterns visual stimulus.2. The system of claim 1, where said device is used to derive anelectroretinogram signal from the eye.
 3. The system of claim 1, wheresaid visual stimulus is a multifocal visual stimulus and said devicedisplays the different multifocal visual stimulus directly to each ofthe two eyes.
 4. The system of claim 1, where said visual stimulus is aflash stimulus.
 5. The system of claim 1, where said visual stimulus isa pattern stimulus.
 6. The system of claim 1, where said visual stimulusvaries in luminance, color or stimulus duration to elicit said retinalresponses.
 7. The system of claim 1, where said device comprises aliquid crystal display or plasma screen adapted to present said visualstimulus.
 8. The system of claim 1, wherein said software is adapted toscale said overall spontaneous brain activity levels for saidelectrophysiological assessment of the visual function of the eye. 9.The system of claim 8, wherein said software is adapted to generate ascaling factor from said spontaneous brain activity levels and scalesaid signals by said scaling factor for said electrophysiologicalassessment of the visual function of each of the two eyes.
 10. Thesystem of claim 1, wherein said device is a head-mounted stereo display.11. The system of claim 10, wherein said head-mounted stereo displaycomprises virtual reality goggles.
 12. The system of claim 1, whereinsaid signals comprise: first sub-signals representative of retinalresponses of each of the two eyes of a subject resulting fromstimulation of said eye by a binocular multifocal visual stimulus:second sub-signals representative of the subject's electroencephalogramlevels during the stimulation of each of said two eyes; and thirdsub-signals comprising alpha-rhythm spikes or electrocardiogram signals;wherein said software comprises: means for identifying and removing thethird sub-signals from the signals; means for determining a scalingfactor from the second sub-signals: means for scaling the firstsub-signals by the scaling factor to provided scaled first sub-signals;and means for analyzing said scaled first sub-signals to provide aelectrophysiological assessment of each of the two eyes.
 13. The systemof claim 1, where said software is adapted to scale said signalsrepresentative of said retinal responses according anelectroencephalogram scaling factor, which excludes alpha rhythm spikesor electrocardiogram signals in the signals identified by Fourier powerspectrum analysis.
 14. The system of claim 1, further comprising meansfor operatively utilizing an algorithm for driving said visual stimulus.15. The system of claim 1, wherein the device comprises the electrodes.16. The system of claim 1, where each said sequences of said visualstimulus is presented to a corresponding portion of the visual field ofeach of the two eyes.
 17. The system of claim 1, forelectrophysiological assessment of two eyes simultaneously such that thesignals for each eye are obtained under the same conditions in terms ofvisual attention and extraneous noise levels.
 18. The system of claim 1,wherein the device is adapted to be mounted on the head.
 19. The systemof claim 1, wherein the device is a stereo display device.
 20. Thesystem of claim 1, further comprising means for recording the signalsobtained from the electrodes.
 21. The system of claim 1, wherein thesoftware is configured to analyze the recorded signals to provide theelectrophysiological assessment of the visual function of each of thetwo eyes.
 22. A system of simultaneous electrophysiological assessmentof two eyes of a head, the head having a scalp, each of the two eyeshaving a visual field, the system comprising: a device adapted to bemounted on the head and configured to simultaneously stimulate differentportions of each of the visual fields of each of the two eyes with avisual stimulus comprising sequences of different timing or character;electrodes adapted to be placed on the scalp and adapted to obtainsignals representative retinal responses of each stimulated portion ofeach of the two eyes to the visual stimulus in each of the stimulatedportions of the visual field, wherein a signal representative of each ofthe stimulated portions of the visual field of each of the two eyes areobtained simultaneously; and software adapted to correlate differentparts of the visual field of each of the two eyes with the retinalresponses of each respective eye to the visual stimulus.
 23. The systemaccording to claim 22, wherein the software is configured to produce amap of the visual field of each of the two eyes.
 24. A method forobjective electrophysiological assessment of visual function of asubject, the method comprising: (a) providing the system of claim 1, andplacing the device on the head of the subject; (b) placing theelectrodes on a scalp of the subject; (c) connecting said device to acomputer which generates an algorithm for driving said stimulus; (d)generating said stimulus; (e) recording the resultant retinal orcortical responses generated as a result of the stimulus, wherein theresponses from each of the different parts of the visual field of eacheye are recorded simultaneously; (f) amplifying and analyzing saidresponses; and (g) as a result of said analyzing, forming a map of thevisual function of each eye.
 25. The method of claim 1, where saiddevice is used to derive a signal from cortical visual evokedpotentials.
 26. The method of claim 1, where said device is used toderive an electroretinogram signal from each eye.
 27. The method ofclaim 1, where said device shows any type of multifocal stimulationdirectly to the eye.
 28. The method of claim 1, where the stimuluspresented in said device is a flash stimulus.